Hot flashes are a primary symptom of the female menopause that greatly impairs quality of life. Despite the considerable problem hot flashes pose for a large number of women, especially given decreased use of hormonal based therapies to treat hot flash symptoms, knowledge regarding the mechanisms of hot flash symptoms is greatly disproportional relative to the extent of the problem. The primary objective of this proposal is to examine mechanisms of cutaneous vascular, sweating, and systemic hemodynamic responses during hot flashes. The signal responsible for elevations in skin blood flow and sweating during a hot flash is not entirely clear and may be neural in origin. Using the innovative technique of multifiber recordings of postganglionic skin sympathetic nerve activity (SSNA) concurrently with skin blood flow and sweat rate measurements SPECIFIC AIM #1 will test the hypothesis that SSNA increases, concomitant with elevations in skin blood flow and sweating, during a hot flash and that the magnitude of the increase in SSNA is directly related to the magnitude of the rise in skin blood flow and sweating. Changes in skin blood flow during a hot flash may occur through modulation of: i) a sympathetic vasoconstrictor system, ii) a separate sympathetic cholinergic active vasodilator system, and/or iii) local factors related to nitric oxide (NO);while increases in sweating during a hot flash may occur upon excitation of cholinergic sympathetic nerves. SPECIFIC AIM #2 will test the hypothesis that withdrawal of sympathetic vasoconstrictor activity, increases in sympathetic cholinergic active vasodilator activity, and/or factors related to NO mediate increases in skin blood flow during a hot flash. Furthermore, this specific aim will test the hypothesis that sweating during a hot flash occurs through cholinergic sympathetic stimulation. These questions will be evaluated using the novel technique of intradermal microdialysis to locally deliver pharmacological agents coupled with continuous assessment of skin blood flow and sweating. In a subset of subjects blood pressure decreases during a hot flash, perhaps due to pronounced increases in cutaneous vascular conductance. Furthermore, symptoms of a hot flash have been reported to be similar to systemic sodium nitroprusside administration (an NO donor that increases cutaneous vascular conductance and lowers blood pressure). Together, these observations raise the possibility that symptoms of a hot flash may be associated with an "NO surge". Therefore, SPECIFIC AIM #3 will test the hypothesis that systemic inhibition of NO synthase reduces the frequency as well as magnitude of objective responses of hot flashes. Upon completion of the proposed work a greater understanding of pre- and post-synaptic mechanisms causing increases in skin blood flow and sweating during a hot flash will be obtained. Moreover, potential mechanisms that modulate blood pressure during hot flashes will be identified. These findings will provide vital information to the health care community that could aid in the development of non-hormonal treatments to decrease the frequency and ameliorate symptoms of hot flashes. Public Health Relevance Statement: Hot flashes are one of the most significant physiological symptoms of the female menopause that greatly impairs the quality of life. Despite the considerable problem hot flashes pose for a large number of women, especially given decreased use of hormonal based therapies to treat hot flash symptoms, relatively little is known regarding the mechanisms of these symptoms. The completion of the proposed work will provide important information regarding mechanisms of skin blood flow, sweating, and blood pressure responses during hot flashes to the health care community that could aid in the development of non-hormonal treatments to reduce hot flash frequency and related symptoms.